Use suggest-override to compilation of polymorphism exercise

code/polymorphism/Makefile

@@ -5,10 +5,10 @@ clean:
 	rm -f *o *so trypoly *~ trypoly.sol
 
 libpoly.so: Polygons.cpp Polygons.hpp
-	$(CXX) -g -Wall -Wextra -shared -fPIC -o $@ $<
+	$(CXX) -Wsuggest-override -g -Wall -Wextra -shared -fPIC -o $@ $<
 
 trypoly : trypoly.cpp libpoly.so
-	$(CXX) -g -Wall -Wextra -o $@ $^
+	$(CXX) -Wsuggest-override -g -Wall -Wextra -o $@ $^
 
 trypoly.sol : solution/trypoly.sol.cpp libpoly.so
 	$(CXX) -g -Wall -Wextra -I. -o $@ $^